Self-foaming hot melt adhesive compositions and methods of making and using same

ABSTRACT

The present invention relates to self-foaming hot melt adhesive compositions and methods of making and using the same. Self-foaming hot melt adhesive compositions are formed by admixing a dispersion concentrate including a chemical blowing agent and a compatible carrier (liquid or molten) with a molten base hot melt adhesive composition at a temperature below the decomposition temperature of the chemical blowing agent. The resolidified material is processed through a device that heats the material above the decomposition temperature of the chemical agent and cools it below such temperature before being dispensed. The device preferably includes sensors and a controller configured to prevent the material from accumulating an adverse thermal history during processing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/864,066, filed Jan. 8, 2018 (now U.S. Pat. No. 10,279,361 B2), whichapplication was a continuation-in-part of U.S. application Ser. No.15/500,747 (now U.S. Pat. No. 9,884,333 B2), which was filed on Jan. 31,2017 as a U.S. national stage of International App. No. PCT/US15/45566,filed Aug. 17, 2015, and claims priority to U.S. Provisional App. Ser.No. 62/038,321, filed Aug. 17, 2014.

BACKGROUND OF INVENTION Field of Invention

The present invention relates to self-foaming hot melt adhesivecompositions and methods of making and using the same. Moreparticularly, the invention relates to self-foaming thermoplastic hotmelt compositions, methods of manufacturing a self-foaming thermoplastichot melt compositions, processing apparatus for activating self-foamingthermoplastic hot melt compositions and methods for adhesively bondingone or more substrates together using self-foaming thermoplastic hotmelt compositions.

Brief Description of Related Art

Foamed adhesives have closed cell gas bubbles uniformly distributedthroughout the matrix. There are numerous benefits to the use of foamedhot melt adhesives including reduced adhesive consumption for equivalentbond performance, longer adhesive open time, lower BTU content perequivalent volume of adhesive, decreased weight per bond leading tolower cost and lower energy consumption. Various foam hot meltcompositions and methods of making same are described including, forexample, in U.S. Pat. Nos. 4,200,207, 4,059,714, 4,059,466, 4,555,284and in WO 2013/078446.

A known method to produce hot melt foam is to meter and mix an inert gasinto the molten hot melt at elevated pressure, for example, 300 psi andabove. The gas dissolves into the hot melt under pressure but createsfoam when the molten material is dispensed from the pressurizeddispensing equipment into standard atmospheric pressure. Unfortunately,this mechanical process does not produce consistent and uniform foamdensity.

U.S. Pat. No. 4,059,714 teaches use of a pump as described in U.S. Pat.No. 4,200,207. This pump has two stages wherein a gas is supplied to thesecond stage to be mixed with hot melt, pressurized, and ultimatelyproduce foamed hot melt when dispensed into atmospheric pressure. Inpractice, it is known that cavitation occurs in the second stage of thepump, which causes it to wear rapidly. As the pump wears, the qualityand density of the foam decreases, thus requiring frequent costly repairor replacement of the pump. This process requires a recirculating loopthat returns non-dispensed hot melt to the second stage of the pump.Recirculation is achieved with heated return hoses which are expensiveand cumbersome. Material being returned to the second stage of the pumpcontributes to the cause of non-uniform foam density.

U.S. Pat. No. 4,059,466 describes the benefits of foamed hot melt indetail. The claims of this patent define a method of bonding withthermoplastic adhesive by “heating solid thermoplastic adhesive and ablowing agent”, then pressurizing said material, heating it to thedecomposition temperature of the blowing agent then dispensing themolten hot melt into standard atmospheric pressure wherein it expandsinto a closed cell foam. This process is not used in industry and hasnot gained commercial acceptance due to several technical obstacles,including:

-   -   a) The solid thermoplastic adhesive granulate and the blowing        agent powder exists in extremely different particle sizes. When        these components are mixed together the powdered blowing agent        is randomly distributed throughout the hot melt granulate.        Therefore, some portions of the hot melt have no blowing agent        while other portions have very high concentrations of blowing        agent. The non-uniform distribution of blowing agent causes        extreme variability in foam density making it commercially        unacceptable. Those portions of hot melt with a high        concentration of blowing agent expands in such great volume that        they cause the foam to collapse and also produce air gaps and        voids in the extruded material. Similarly, portions of the hot        melt with no blowing agent do not foam at all.    -   b) The blowing agent powder settles by gravity making direct        contact with the heated tank floor and tank walls. Some of this        blowing agent powder decomposes even before the granulated hot        melt becomes molten. This further contributes to unacceptable        foam uniformity in commercial use.    -   c) U.S. Pat. No. 4,059,466 describes a melt temperature of        250° F. for the hot melt blowing agent powder mix. This is an        impractically low temperature to accommodate high speed        automatic application of hot melt adhesives. At 250° F., the        melt rate of most hot melts is below the demand rate of        automated production lines.    -   d) Hot melt application equipment is generally accessible to        production line personnel. It is common place for these        individuals to change equipment, temperature and pressure        settings. The blowing agent specified in this patent begins to        decompose and generate gas at temperatures of 350° F. and above.        As shown on FIG. 1, which is a publicly available graph showing        the decomposition rate of activated azodicarbonamide (Celogen®        AZ-130) in a dioctyl phthalate (“DOP”) plasticizer material, the        decomposition rate is a function of time at temperature. The        method disclosed in this patent has no provision to monitor the        accumulated thermal history of the molten hot melt blowing        agent mix. Therefore, when the accumulated thermal history        reaches the decomposition point, hot melt foam will be generated        in a melt tank open to atmosphere. When foam expansion occurs in        the melt tank, the foam overflows from the tank contaminating        the surrounding area presenting dangerous burn hazards and        incinerating electronic controls.

U.S. Pat. No. 4,059,466 also describes a method of producing a hot meltfoam by first heating solid hot melt particles and a blowing agentpowder blend to a temperature at which the blend becomes molten, butbelow the decomposition temperature of the blowing agent (T-1), thenpumping and pressurizing said molten composition through a heat sourceto increase its temperature to the decomposition temperature of theblowing agent (T-2), then dispensing said composition into atmosphericpressure upon which it expands into a hot melt foam. This patentspecifies an adhesive application temperature of approximately 375° F.,which is below the temperature needed to decompose 100% of the blowingagent. At 375° F., the amount of gas evolved will depend on the lengthof time the material is held at that temperature. Therefore, foamdensity will change when material consumption rates change.

Chemical blowing agents decompose to produce a gas at elevatedtemperatures. Decomposition rates are a function of time andtemperature. As temperature increases, the length of time needed toactivate and decompose the blowing agent decreases (see, e.g., FIG. 1).

FIG. 1 reveals that at temperatures of 383° F. and below, not all of theactivated azodicarbonamide decomposes, even after 30 minutes attemperature. Unless temperatures of 392° F. and above are achieved, theamount of activated azodicarbonamide that decomposes at lowertemperatures will vary. Therefore, the foam density resulting from thevolume of gas produced depends upon the length of time the material isheld at any given temperature below 392° F.

In automated hot melt applications, the amount of hot melt consumed perunit time constantly changes as production lines change speed or duringidle time; for example, to change dispensing nozzles, to fix line jams,for lunch breaks, or any other situation that interrupts the rate ofmaterial consumption.

Because of this variability in hot melt consumption, any decompositiontemperature below 392° F. will result in inconsistent and changeableblowing agent decomposition and the amount of gas evolved. This, inturn, results in variability in the density of the hot melt foamproduced. Variable foam density is unacceptable in automated hot meltproduction lines because variable volume of adhesive deposited couldcause bond failure, changeable set time (too fast or too slow), andvariable bond surface area.

Also, at temperatures of 375° F. and above, hot melt are subject tothermal degradation, loss of physical properties and lower adhesiveperformance. In addition, at these elevated temperatures most hot meltshave a viscosity that is too low to support formation of acceptable foamdue to cell coalescence, cell breakage and foam shrinkage.

BRIEF SUMMARY OF THE INVENTION

To avoid thermal degradation of self-foaming hot melt adhesivecompositions that may occur at the elevated temperatures needed toachieve complete decomposition of the blowing agent, it is necessary tocool the hot melt. There are two conditions at which cooling the hotmelt below the decomposition temperature of the blowing agent isnecessary.

The first condition applies to the heating apparatus utilized toincrease the temperature of the hot melt blowing agent admixture to thedecomposition temperature of the blowing agent. Hot melt will begin todegrade if held at blowing agent decomposition temperatures for extendedtime periods which occurs if the rate of hot melt consumption slows orstops due to production line stoppages. When this happens, thetemperature of the hot melt must be actively reduced.

The second condition under which the hot melt temperature should belowered below the decomposition temperature of the blowing agent isprior to being dispensed onto the substrates being bonded. The hot meltdeposition temperature must be low enough to prevent foam cellcoalescence, cell breakage and foam shrinkage. The hot melt depositiontemperature may be further reduced to decrease BTU content of theadhesive dispensed so that the time it takes to solidify and form a bond(set time) can be lessened.

The present invention provides simplified, cost-efficient methods toproduce self-foaming hot melt adhesive compositions, and apparatus andmethods for producing and dispensing the same. In one embodiment, thepresent invention provides a device with the dual capability of bothheating and/or cooling molten hot melt. It functions to increase amolten admixture of hot melt and blowing agent to the decompositiontemperature of the blowing agent and, when necessary, to decrease thetemperature of hot melt to avoid thermal degradation and provide foroptimal hot melt dispensing temperature.

In one embodiment of the invention, the surface of micronized blowingagent particles is coated prior to being incorporated into a hot meltmaterial. Said coating is a liquid that is chemically compatible withthe hot melt. The liquid coating prevents agglomeration of themicron-sized blowing agent particles and aids in its uniformdistribution into the molten hot melt during its manufacture. Thus, inone embodiment, the invention includes surface coating the micronizedblowing agent particles with one or more low viscosity ingredients ofany given hot melt formulation at a temperature below the decompositiontemperature of the blowing agent to form a concentrate, and thenincorporating said blowing agent concentrate into the molten hot meltduring its manufacture.

Another aspect of this invention is to monitor and control thetemperature and thermal history of a self-foaming molten hot meltblowing agent admixture at the time of use, wherein the melt temperatureand thermal history of the molten hot melt remains below thedecomposition of the blowing agent prior to it being pumped, pressurizedand heated to a second temperature at which the blowing agentdecomposes.

Yet another object of this invention is to provide a singular apparatuswith the capability to heat a molten hot melt blowing agent admixture(T-1) to the decomposition temperature of the blowing agent (T-2) thento cool, the gas containing hot melt to a temperature below thedecomposition temperature of the blowing agent (T-3), and thendispensing said gas containing hot melt into atmospheric pressurewherein it expands into a foam.

The present invention is also directed to the preparation ofself-foaming hot melt adhesive materials, and a process to activate anddispense hot melt wherein it expands into a foamed hot melt adhesive.Self-foaming hot melts are made by first preparing a concentrate ofmicronized blowing agent powder by coating it with a liquid component orlow viscosity molten component of a given hot melt formulation byutilizing high shear mixing. Said blowing agent concentrates are thenadmixed into a molten hot melt at a temperature below the decompositiontemperature of the blowing agent at a final blowing agent concentrationof 0.1 to 8.0 percent. This blowing agent dispersion concentrate isincorporated into the hot melt during its manufacture at a blendingtemperature below the decomposition temperature of the blowing agent.Incorporation of the blowing agent as a concentrated micronizeddispersion with one of the formulation ingredients ensures uniformdistribution of blowing agent particles in the hot melt. This processrequires far less shear mixing that generates heat exposure andprocessing time that would otherwise be required if blowing agent powderwere added directly to the molten hot melt ingredients during the normalhot melt manufacturing process. It also avoids premature decompositionof blowing agent that can occur with high shear mixing.

The foregoing and other features of the invention are hereinafter morefully described below, the following description setting forth in detailcertain illustrative embodiments of the invention, these beingindicative, however, of but a few of the various ways in which theprinciples of the present invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the accompanying drawing figures, please note that:

FIG. 1 is graph (prior art—publicly available) showing the decompositionrate of an activated azodicarbonamide (Celogen® AZ-130) in a dioctylphthalate (“DOP”) plasticizer, in which the decomposition rate is shownas a function of time-at-temperature.

FIG. 2 is a perspective schematic view of an exemplary device foractively heating/cooling hot melt compositions in accordance with theinvention;

FIG. 3 is a side section view of a device similar to that shown in FIG.2 to which is attached a manifold; and

FIG. 4 is a side section view showing the devices shown in FIGS. 2 and 3in series.

DETAILED DESCRIPTION OF THE INVENTION

A self-foaming hot melt adhesive composition according to the inventioncomprises an admixture of a base hot melt adhesive composition and oneor more chemical blowing agents. The term “base hot melt adhesivecomposition” refers to a hot melt composition to which the chemicalblowing agent(s) is to be added. Preferably the chemical blowing agentis present at a concentration of from about 0.1% to 8.0% by weight ofthe admixture. More preferably, the chemical blowing agent is presentbetween 1% and 2% by weight of the admixture.

The presently most-preferred chemical blowing agent for use in theinvention is activated azodicarbonamide. However, other chemical blowingagents may be used including, for example,oxybis(benzenesulfonylhydrazide) (OBSH), toulenesulfonylhydrazide,trihydrazinotriazine, p-toulenesulfonyl semicarbazide (TSS), potassiumbicarbonate and sodium bicarbonate blended with citric acid. Some of theless-preferred blowing agents initiate decomposition at temperaturesbelow 300° F., for example: OBSH (decomposition temperature of 284° F.);and sodium bicarbonate citric acid blends decomposition temperatureinitiation at 250° F.). Thus, these blowing agents should not be used insome commercial applications because at the noted decompositiontemperatures blowing agent activation occurs in melting pots typicallyheld at temperatures of 300° F. or above. The majority of commerciallyavailable meltable adhesives must be heated to at least 300° F. so thatthey can flow by gravity into mechanical gear or piston pumps. Ifdecomposition of blowing agent occurs at temperatures below the nominalmelting and flowing temperature of most hot melts, premature foaming ofsaid materials will occur in the melt-holding tank causing saidmaterials to foam and expand in the melting tank. This is a commerciallyunacceptable occurrence causing mechanical pumps to cavitate and becomeincapable of developing sufficient pumping and pressurizing of the melt.

Also, blowing agents that decompose at temperatures above 400° F. shouldnot be used in some commercial applications because polymer compositionscontained in the hot melt formulation thermally degrade at temperaturesof 400° F. and above. Thermal degradation causes polymer chains to breakdown dropping molecular weight, oxidizing, and otherwise decreasing theadhesive and physical properties of the adhesive rendering them useless.

Unactivated Azodicarbonamide does not begin decomposition until reaching380° F., and it is not fully decomposed until reaching 425° F. andabove. Thus, the use of unactivated Azodicarbonamide as a blowing agentin hot melt materials is not preferred, as it could lead to unacceptablepolymer chain breakdown destroying the required physical and adhesiveproperties of the adhesive.

Thus, the presently most preferred blowing agent for meltable adhesivecompositions is activated azodicarbonamide compounded with knowndecomposition accelerators such as zinc stearate, zinc oxide and manyother known accelerators. A commercially available activatedazodicarbonamide is Celogene® AZ-130, which has the ideal decompositiontemperature profile illustrated in FIG. 1.

Chemical blowing agents are supplied commercially in powder form inparticle sizes ranging between 3 and 100 microns (i.e., a preferredrange for use in the invention). These particles often stick together inclumps or agglomerates, which must be broken down before they areincorporated into self-foaming hot melt so as to prevent foam collapse,voids, and non-uniform density of the hot melt foam. Therefore, blowingagent particles must be coated with and dispersed into a carrier, whichcan be a liquid compatible with a given hot melt or a low viscosity,preferably below 1,000 centipoise, molten component of a given hot meltformulation. Said blowing agent can constitute from 5% to 70% by weightof the total blend, preferably 25% to 50%, of the dispersionconcentrate. The dispersion concentrate is preferably prepared by slowlysifting the blowing agent powder into the liquid phase material whilethe liquid is being agitated at a minimum of 500 rpm, or preferably at3,200 rpm, using commercially available high velocity mixers such as aCowels Disperser. The time needed to break down blowing agentagglomerates depends on the specific blowing agent and its concentrationas a percentage of the total dispersion. Commercially available,fineness of grind gauges may be used to determine when the dispersion issufficiently blended. The fineness of grind gauge should reveal that themean particle size in the dispersion is the same as the particle sizespecified by the blowing agent supplier.

Some compatible liquids that may be used to create micronizeddispersions with blowing agents include mineral oil, naphthenic oils andplasticizers. Some low viscosity molten hot melt ingredients used toprepare blowing agent dispersions are wax and tackifiers. Ideally, theviscosity of the finished dispersion would range in viscosity from 100to 3,000 centipoise, but preferably less than 1,000 centipoise.Dispersions made with molten low viscosity components of a given hotmelt should also have a viscosity between 100 and 3,000 centipoise, andpreferably less than 1,000 centipoise, while in the molten state.

There are several known surfactants and nucleating agents thatsignificantly improve foam cell uniformity and stability in certain hotmelts that tend to collapse or deform once they are dispensed and beginto expand into a foam. Many of these surfactants and nucleating agentsare described in U.S. Pat. No. 4,259,402, which is hereby incorporatedby reference in its entirety for such teachings.

Blowing agent dispersion concentrates according to the invention mayalso include the known nucleating agents and surfactants simultaneouslyincorporated into a multi component three-part dispersion concentrate.Preparation of this dispersion concentrate which includes the blowingagent, surfactant(s) and nucleating agent(s), insures uniformdistribution of all of these ingredients so they are in intimate contactwith each other when they are incorporated into the hot melt. Such aconcentrate avoids the multiple steps of independently formingdispersion concentrates of each of the three agents.

A master batch concentrate of these agents assures that each isuniformly distributed and dispersed. This step assures intimate physicalcontact of the nucleating agent and surfactant with each micron sizeblowing agent particle as it decomposes into a gas resulting in a stableuniform cell formation.

The dispersion concentrate of blowing agent and carrier is incorporatedinto the base hot melt adhesive composition when the latter is moltenduring normal mixing/blending processes utilized in the manufacture ofconventional hot melt adhesives. The temperature of the hot melt duringthe process of dispersion incorporation must be lower than thedecomposition temperature of the specific blowing agent. If the blowingagent dispersion concentrate is introduced to a hot melt batch at atemperature near or above the decomposition temperature of the blowingagent, unpredictable amounts of gas will be generated causing somefoaming to occur in the hot melt mixing vessel. This would potentiallyruin an entire production batch.

Because normal mixing procedures used to manufacture hot melt sometimescreate heat, it is preferable to hold the hot melt temperature 5% to 10%below the decomposition temperature of the blowing agent whileincorporating the blowing agent dispersion. For example: activatedazodicarbonamide (Celogen® AZ-130) begins to decompose at approximately338° F. Thus, the temperature of the base hot melt batch to which it isintroduced should not exceed about 320° F. Blowing agent benzenesulfonylhydrazide (OBSH), begins to decompose at 302° F. Therefore, thetemperature of the base hot melt batch should not exceed 280° F. whileincorporating an OBSH blowing agent dispersion.

As noted above, mixing is conducted at high shear to ensure uniformdistribution of the chemical blowing agent in the base hot melt adhesivecomposition. Once sufficient mixing has occurred, the material is cooled(actively or passively) and processed for end use (e.g., pelletized orplaced into suitable containers such as drums, as is known in the art).This material may sometimes be referred to herein as a “self-foaming hotmelt adhesive composition” and/or as a “blowing agent hot meltadmixture.”

It is well known in the hot melt industry that thermal degradation andthe resulting loss of physical properties is a major problem in theprocess of melting and applying hot melt adhesives. Breakdown of themolecular chains develop as a result of laminar flow along the sidewalls of hot melt equipment and hoses. The thermal degradation processbegins over time and is accelerated as temperatures increase, typicallyfor most hot melts, above 350° F. This phenomenon is particularlyamplified when hot melt blowing agent admixtures are heated to thehigher temperatures necessary to decompose the blowing agent containedin the hot melt admixture. Therefore, to eliminate the potentialdevelopment of the thermal degradation of hot melt in heat exchangerdevices used to decompose blowing agents it is necessary to activelycool said heat exchanger to lower temperatures whenever material flowstops.

FIG. 2 illustrates an embodiment of the present invention, which is adevice 10 that can actively heat or cool hot melt adhesive compositions.The device 10, which is sometimes referred to herein as a “heatexchanger”, is connected to a hot melt hose 20 that supplies hot melt ina molten, but not activated, state from a source such as a melt kettle(not shown). The molten hot melt enters the device 10 through an inlet30 and passes through a heat transfer coil 40. The hot melt is heated inthe heat transfer coil 40 to its activation temperature (i.e., atemperature at which the chemical blowing agent complete decomposes intoa gas). Decomposition of the chemical blowing agent causes the hot meltmaterial to pressurize in the heat transfer coil 40. Once activated, theactivated hot melt material flows out of an outlet 50 to another device10′ according to the invention (e.g., as shown in FIG. 4), to a manifold(e.g., as shown in FIG. 3), or directly to hot melt dispensingequipment.

The heat transfer coil 40 is encased within a body 60, which ispreferably made of aluminum but could be made of other suitablematerials. The body 60 also encases a heater 70, which supplies heat toheat the hot melt material in the heat transfer coil 40. The heater 70is controlled by a controller 80, which energizes and de-energizes theheater 70 based on information or data received from a sensor 90.

The body 60 also encases a cooling coil 100. The cooling coil 100receives cooling air or water (or other flowable cooling material) thatis supplied by a cooling line 110 through a cooling inlet 120. Flow ofthe cooling material is controlled by a solenoid 130, which is incommunication with the controller 80. When the temperature is determinedto be too high in the body 60, the solenoid 130 opens allowing coolingmaterial from a cooling material source (not shown) to flow from acooling material supply line 140 through the solenoid, the cooling line110 and cooling inlet 120 into the cooling coil 100 to cool the materialin the heat transfer coil 40.

Thus, to use the device 10 shown in FIG. 2 a molten hot melt blowingagent admixture at a temperature below the decomposition temperature ofthe blowing agent T-1 is pumped under pressure through hot melt hose 20to inlet 30 such that it then flows through heat transfer coil 40 beforeexiting through outlet 50. The molten material in the heat transfer coil40, which is contained in the body 60, is heated to the decompositiontemperature of the blowing agent, T-2, by heater 70, which is controlledby controller 80 in response to temperature data received from sensor90. Hot melt containing dissolved gas at decomposition temperature T-2exits the apparatus at outlet 50. Controller 80 monitors material flowin and out of heat transfer coil 40 utilizing software algorithms thatdetect the rate of temperature change as measured by sensor 90. Whenmaterial flow stops for longer than predetermined programmed parametersknown to cause thermal degradation of the hot melt, temperaturecontroller 80 turns off electrical power to heater 70 and turns onelectrical power to solenoid 130 causing cooling air or water to flowthrough cooling coil 100 lowering the temperature of the material in theheat transfer coil 40 within the body 60. This cooling mode continuesuntil a pre-established cooling temperature is achieved. Whentemperature sensor 90 detects material flow has resumed, solenoid 130 isde-energized, the cooling mode stops and heater 70 is powered on,returning the apparatus to heater mode.

It is also known in the art that foamed hot melt adhesives do notsolidify or “set” as fast as unfoamed hot melt adhesives because theentrained gas cells act as insulators that slow the rate of heat loss.Therefore, a further advantage of a heat exchanger with the capabilityof both heating and cooling hot melt is that it can be used to coolactivated hot melt material to any lower temperature thus reducing itsBTU content so set time of the dispensed adhesive can be decreased asdesired.

FIG. 3 shows a device 10′, which is identical to that shown in FIG. 2except that it operates to cool activated hot melt (e.g., as receivedfrom a device according to FIG. 2) before it is dispensed or deposited.Referring now to FIG. 3, hot melt under pressure containing entrainedgas at T-2 is received through hose 20 (preferably heated) through inlet30 and flows through heat exchange coil 40 until it exits through outlet50. Again, the heat exchange coil 40 is encased within body 60. A heater70 is present in the event that heat needs to be supplied to thematerial. But the device 10′ is particularly configured to supplycooling material through cooling coil 100 to reduce the temperature ofthe activated hot melt material to the final desired hot melt depositiontemperature. Sensor 90 communicates with controller 80 to determine thetemperature of the material entering the body 60. If the hot meltmaterial temperature introduced at or near inlet 30 is higher than thedesired hot melt deposition temperature, sensor 90 communicates thisinformation to controller 80, which responds by turning off power toheater 70 and turning on power to solenoid 130 causing cooling air orwater to flow through cooling coil 100 until the desired hot meltdeposition temperature is achieved. A manifold 150 is optionallyconnected at the outlet 50. The manifold 150 allows activated hot meltmaterial at the predetermined dispensing temperature (T-3) to besupplied to a plurality of dispensers in fluid communication with themanifold 150.

The present invention is also directed to a method of controlling andmonitoring the temperature and accumulated thermal history of a blowingagent hot melt admixture heated to become molten at a temperature belowthe decomposition temperature of the blowing agent in hot melt tanks orvessels that are open to atmosphere. As shown on FIG. 1, activatedazodicarbonamide will begin to decompose at 338° F. in just 5 minutes.Blowing agent decomposition in vessels open to atmosphere are exothermicand self-accelerating. Once decomposition is initiated hot melt blowingagent admixtures have the potential to initiate foam expansion andover-flow from hot melt vessels or tanks, thus contaminating thesurrounding area. This occurrence presents a burn hazard andhousekeeping nightmare that is unacceptable in an industrialenvironment. If the accumulated thermal history of hot melt blowingagent admixtures held molten in open vessels is not monitored andcontrolled, premature decomposition of the blowing agent and foamoverflow is likely to occur.

This invention provides an electronic control algorithm with temperatureinput provided by a sensor located in the melt vessel. Specificalgorithms are based on the specific decomposition characteristics ofthe particular blowing agent admixture being monitored. In the specificcase of activated azodicarbonamide (Celogen® AZ-130), one suitablecontrol algorithm program could be:

-   -   Hot melt temperature 325° F.—No action taken;    -   Hot melt temperature 330° F. and above for more than 10        minutes—System Alarm activated—if no corrective action is taken        within 10 minutes of System Alarm, tank heater automatically        shut down until material temperature drops to 325° F.;    -   Hot Melt temperature 340° F. and above for more than five        minutes—System Alarm activated—if no corrective action is taken        within 3 minutes of System Alarm, tank heater automatically shut        down until material temperature drops to 325° F.; and    -   Hot Melt temperature 345° F. and above—Immediate System Alarm        activated and tank heater shut down for 30 minutes or until        material temperature drops to 325° F. or below.

It will be appreciated that the specific times and temperatures can beadjusted based on the composition of the material being utilized, thedelay period before action desired, etc. In all of the noted faultconditions, the heater will be returned to Power ON only after themolten hot melt blowing agent admixture cools to a predeterminedtemperature below the decomposition time-temperature profile of thespecific blowing agent in use.

Automated production lines must have consistent and uniform adhesivebead dimensions and adhesive volume applied to the substrates beingbonded in order to ensure reliable adhesive bonds. When hot melt blowingagent admixtures are used to create hot melt foam, it is imperative that100% of all blowing agent be decomposed before the adhesive is dispensedonto a substrate. Incomplete or variable blowing agent decompositioncauses inconsistent foam density which is unacceptable in automatedproduction lines.

As shown in FIG. 1, activated azodicarbonamide must reach a temperatureof 392° F. or above for 11 minutes at atmospheric pressure to fullydecompose. The decomposition rate of activated azodicarbonamide isaccelerated if decomposition takes place in a hydraulically closedsystem wherein pressure and heat generated by the exothermic reactionadd to the reaction rate. However, the temperatures required to achievetotal decomposition as shown on FIG. 1 remain the same.

It is known that thermoplastic hot melts degrade and lose their physicalproperties when exposed to elevated temperatures for extended timeperiods. Therefore, it is necessary to limit the length of time a givenamount of hot melt is held at blowing agent decomposition temperaturesto avoid thermal degradation. The elevated temperature required to reachcomplete decomposition of the blowing agent is also the temperaturesthat will, over time, initiate thermal degradation of hot melt.

The rate of hot melt consumption in automated production changes andsometimes stops for unpredictable time intervals; for example, if aproduction line jams or during lunch break shift changes, overnightshutdown and so forth. When hot melt consumption stops, the materialpresent in the apparatus used to increase the temperature of a hot meltblowing agent admixture to decomposition (T-2) should have the abilityto discontinue heating and begin cooling the material to avoid thermaldegradation in response to changes in hot melt consumption. Thisprocedure also prevents char build-up; i.e., degraded hot melt, on thewalls of the material flow path. Over time, char could build to restrictmaterial flow. Char particles also break off and plug dispensingnozzles.

In order to eliminate the possibility of thermal degradation and also toprovide the capability to reduce T-2 temperature prior to dispensing hotmelt containing dissolved gas, the present invention utilizes anapparatus that has the dual capability to heat or cool hot melt flowingthrough it. They can be linked in series, as is shown in FIG. 4.

With reference to FIG. 4, molten hot melt below the decompositiontemperature of the blowing agent (T-1) is pumped into a first device 10,where it is heated to the decomposition temperature of the blowing agent(T-2). In normal production, the heated hot melt material continues toflow out of the first device 10 and into a second device 10′, whichcools the gas-containing hot melt to a temperature below thedecomposition temperature of the blowing agent (T-3). However, if hotmelt material flow stops due to line jams or other causes, the heater inthe first device 10 is turned off and cooling air or water is introducedto cool the stagnant gas-containing hot melt to a lower temperaturethereby preventing degradation of the hot melt. The controllers makeappropriate temperature adjustments in the second device 10′, asdescribed below, during the period of shut-down. When normal productionrestarts and hot melt material begins to flow again, the controllersreturn the devices 10, 10′ to their normal production state.

Thus, the first device 10 is configured to heat the hot melt materialflowing through it to the decomposition temperature (T-2) in continuousflow production, but would enter into a cool mode if production flowstopped. The second device 10′ in series would cool the material flowingthrough it from decomposition temperature (T-2) to the lower dispensingtemperature (T-3) during normal continuous flow production, but wouldturn on the heater and maintain the temperature (T-3) for the materialin the system until production restarts and newly heated material isflowing into the second device 10′. If production stops, then cooling onthe second device 10′ has to stop and heating has to be initiated to ahold temperature (T-3), otherwise material in the second device 10′would solidify. This circumstance can occur during line stops for lunchbreaks etc. The use of two devices in series allows for higherthroughout, while also allowing for interruptions during production.

The following examples are intended only to illustrate the invention andshould not be construed as imposing limitations upon the claims.

Example A-1—Formation of Blowing Agent Dispersion Concentrate—Liquid

A 30% concentration of activated azodicarbonamide (Celogen® AZ-130)average particle size 10 microns from Galata Chemical, Danbury, Conn.,admixed with Calumet Calsol 550 (hydro-treated naphthenic petroleum oilsupplied by Calumet Specialty Products LLC, Indianapolis, Ind.) wasprepared at room temperature using a high speed blender at 3,200 rpm for8 minutes. The resulting dispersion had a viscosity of 1,200 centipoise.

Example A-2—Formation of Self-Foaming Hot Melt Adhesive Composition

The blowing agent dispersion concentrate formed in Example A-1 was addedand blended into a metallocene base hot melt adhesive compositionobtained from H. B. Fuller at a temperature of 300° F., which is abovethe melt temperature of the base hot melt adhesive composition but belowthe decomposition temperature of activated azodicarbonamide. The precisecomposition of the base hot melt adhesive composition is proprietary tothe manufacturer and is not known by applicant. The “let down” rate orfinished blowing agent concentration for the mixture was 1.25% byweight. Mixing was accomplished using a 1 horsepower drill at 800 rpmwith a 2½″ spiral mixing head in a 12 quart mixing vessel for 5 minutes.The resulting material was poured into non-stick molds havingapproximate dimensions of 8″×4″×3″, and allowed to cool and re-solidifyinto a self-foaming hot melt adhesive composition.

Example A-3—Activation and Use of Self-Foaming Hot Melt AdhesiveComposition

The self-foaming hot melt adhesive composition from Example A-3 wasmelted in a LTI Dynatec hot melt tank at 320° F. Once molten, it waspumped at 400 psi through a heat exchanger such as shown in FIGS. 2 and3 to elevate its temperature to 410° F., thereby decomposing all of theactivated azodicarbonamide. It was then pumped through a coolingapparatus reducing its temperature to 350° F. and dispensed intoatmospheric pressure producing a hot melt foam with a bulk density 50%below the bulk density of the identical hot melt without blowing agent.The dispensed hot melt foam was used to join combinations of thefollowing substrates together (and to each other): cardboard; cereal boxcartons; filter paper; beverage carton stock; and clay-coated craftpaper. Room temperature tear tests on bonded substrates revealed 100%fiber tear on all surfaces in contact with the adhesive.

Example B-1—Formation of Blowing Agent Dispersion Concentrate—Solid

A 30%, by weight, concentration of an activated azodicarbonamide (GALATACHEMICAL ACTAFOAM 130) in molten (200° F.) wax (CALUMET FR-6513) wasprepared using a high speed blender at 3,200 rpm for 4 minutes. Theresulting blowing agent concentrate was cooled to room temperature andsolidified.

Example B-2—Formation of Self-Foaming Hot Melt Adhesive Composition

The dispersion concentrate formed in Example B-1 was melt-blended intothe molten ingredients of the same metallocene-based hot melt as used inExample A-2 at a “let down” finish concentration of 1.35%, by weight,activated azodicarbonamide. The same processing conditions and equipmentas used in Example A-2 were used.

Example B-3—Activation and Use of Self-Foaming Hot Melt AdhesiveComposition

The self-foaming hot melt adhesive composition prepared in Example B-2was melted in a LTI Dynatec Hot Melt Tank and processed in the samemanner as in Example A-3. The resulting foam bulk density was 50% lowerthan the identical hot melt without blowing agent. The dispensed hotmelt foam was used to join combinations of the following substratestogether (and to each other): cardboard; cereal box cartons; filterpaper; beverage carton stock; and clay-coated craft paper. Roomtemperature tear tests on bonded substrates revealed 100% fiber tear onall surfaces in contact with the adhesive.

Example C-1—Formation of Blowing Agent Dispersion Concentrate—Liquid

Fifty percent concentration of an activated azodicarbonamide (GALATACHEMICAL ACTAFOAM AZ-130) admixed with medium weight generic mineral oilwas prepared in a Hobart Planetary Mixer at 240 rpm for 10 minutes atroom temperature. The resulting dispersion concentrate was a thick pastewith a rheology similar to applesauce.

Example C-2—Formation of Self-Foaming Hot Melt Adhesive Composition

The dispersion concentrate formed in Example C-1 was melt-blended intoBostik 55-606 pressure-sensitive hot melt adhesive at an activatedazodicarbonamide “let down” concentration of 1.5% by weight. The mixingconditions and equipment used were the same as in Examples A-2 and B-2.The molten material was cooled to room temperature in solid cast blocks.

Example C-3—Activation and Use of Self-Foaming Hot Melt AdhesiveComposition

The self-foaming hot melt adhesive composition produced in Example C-2was heated in a HMT (Hot Melt Technologies, Rochester, Mich.), hot melttank and heated to a molten temperature of 310° F. The admixture waspumped and pressurized to 450 psi through a heat exchanger elevating thetemperature to 400° F. and causing the blowing agent to fully decomposeproducing a nitrogen gas solution with the hot melt. This hot melt gassolution was pumped though a 12-foot hot melt hose at 350° F. coolingthe material to 350° F. When dispensed into atmospheric pressure, thepressure-sensitive adhesive produced a foam with a bulk density 50%below the same hot melt without blowing agent. The material was used tobond the same substrates as in Examples A-3 and B-3. Room temperaturetear tests on bonded substrates revealed 100% fiber tear on all surfacesin contact with the adhesive.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and illustrative examples shown anddescribed herein. Accordingly, various modifications may be made withoutdeparting from the spirit or scope of the general inventive concept asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for making a self-foaming hot meltadhesive composition comprising: dispersing a chemical blowing agent ina carrier to form a concentrated micronized dispersion that does notinclude agglomerates of the blowing agent; admixing the concentratedmicronized dispersion into a base hot melt adhesive composition at atemperature above the melt temperature of the base hot melt adhesivecomposition but below a decomposition temperature of the chemicalblowing agent to form an admixture; and cooling the admixture below atemperature at which the admixture solidifies to obtain the self-foaminghot melt adhesive composition in solid form; wherein the chemicalblowing agent is in the form of a powder with an average particle sizewithin the range of 3 to 100 microns, and wherein the carrier is either(1) a liquid that is compatible with the base hot melt adhesivecomposition, or (2) a molten low viscosity component of the base hotmelt adhesive composition.
 2. The method according to claim 1 whereinthe chemical blowing agent is selected from the group consisting ofazodicarbonamide, oxybis(benzenesulfonylhydrazide),toluenesulfonylhydrazide, trihydrazinotriazine, p-toluenesulfonylsemicarbazide, sodium bicarbonate and potassium bicarbonate.
 3. Themethod according to claim 1, wherein the chemical blowing agent isactivated azodicarbonamide.
 4. The method according to claim 3, whereinthe activated azodicarbonamide comprises zinc stearate and/or zincoxide.
 5. The method according to claim 1, wherein the carrier comprisesthe liquid that is compatible with the base hot melt adhesivecomposition, and the liquid comprises mineral oil, naphthenic oilsand/or plasticizers.
 6. The method according to claim 1, wherein thechemical blowing agent comprises from about 5% to 70% of theconcentrated micronized dispersion by weight.
 7. The method according toclaim 1, wherein the chemical blowing agent comprises from about 0.1% toabout 8% of the self-foaming hot melt adhesive composition by weight. 8.The method according to claim 1, wherein the concentrated micronizeddispersion comprises the blowing agent, a surfactant and a nucleatingagent.